1. Field of the Invention
This invention generally relates to shutter apparatuses for optical apparatuses, and more particularly, to a shutter suitable for use in an optical apparatus such as a digital camera or camcorder.
2. Description of the Related Art
Recent years, a shutter apparatus included in an optical apparatus such as a camera or the like is driven by a motor. Cameras have been downsized at a remarkable speed. For instance, a digital camera installed on a mobile phone is particularly downsized. Accordingly, there exists a need for a more downsized shutter apparatus in a camera, and further, a simplified structure of the shutter apparatus.
The shutter apparatus includes a shutter blade that closes a shutter opening at the time of exposure. Generally, multiple sectors are used to close the shutter opening more quickly. As disclosed in Japanese Patent Application Publication No. 2001-117135 (hereinafter, referred to as Document 1), it is known that the shutter apparatus is configured to form a small aperture state by use of an aperture blade having an aperture opening. This shutter apparatus includes multiple shutter blades and the aperture blade.
Japanese Patent Application Publication No. 2000-39646 (hereinafter, referred to as Document 2) discloses the shutter apparatus that forms a fully closed state and the small aperture state by use of two shutter blades. In Patent document 2, two sectors, which are an upper aperture blade and a lower aperture blade, are driven to open and close by a stepping motor. FIG. 5 shows a sector operation described in Document 2. A first sector 101 is pivotally provided with respect to a fixed shaft 102, and a second sector 107 is pivotally provided with respect to a fixed shaft 108. These sectors 101 and 107 are movably arranged in positions that open and close a shutter opening 100 provided in a shutter substrate.
Specifically, an opening 103 is provided in the first sector 101. In the same manner, an opening 109 is provided in the second sector 107. The openings 103 and 109 are pierced by an operation pin 105, and are engaged with each other. Thus, as shown in FIG. 5, it is possible to form a small aperture state, fully closed state, and fully open state by moving the operation pin 105 in a given direction to control the positions of the two sectors 101 and 107. With this configuration, it is possible to form the fully closed state and small aperture state by use of two sectors, thereby enabling the sector structure in the shutter apparatus.
In the shutter apparatus disclosed in the afore-mentioned Document 1, however, the aperture blade is used for forming the small aperture state, yet the aperture blade does not function when the shutter opening is closed. Therefore, this needs multiple shutter blades for exclusive use in the formation of the fully closed state, resulting in an increase of the number of sectors. On the other hand, in the shutter apparatus disclosed in Document 2, it is possible form the fully closed state (close) and the small aperture state with two shutter blades, thereby enabling the structure thereof to be simplified. However, only if the two shutter blades are respectively situated on given positions, the fully closed state or small aperture state can be formed. Therefore, in the shutter apparatus described in Document 2, it is necessary to control the positions of the both shutter blades with high accuracy.
In the shutter disclosed in Document 2, however, the openings 103 and 109 provided in the first sector 101 and the second sector 107 have simple structures. As the operation pin 105 moves upwardly, the above-mentioned first sector 101 and the second sector 107 form the small aperture state, fully closed state, and fully open state. In contrast, if the operation pin 105 moves downwardly from the fully open state, an opposite state is formed. Here, the fully closed state is existent between the small aperture state and the fully closed state.
Now, an inertial force (inertia) works, when the sectors 101 and 107 are moved from given positions to other ones. When the operation pin 105 that is driven by the stepping motor moves the sectors 101 and 107 to the fully closed position from the small aperture position, or when the operation pin 105 moves the sectors 101 and 107 to the fully closed position from the fully open position, which causes the hunting in some cases, according to the inertial force applied to the sectors and brake on the stepping motor side. That is to say, the inertial force is applied onto the sectors 101 and 107, although they stop moving at the fully closed position from a moving state. There is a force that causes the sectors 101 and 107 to oveimn from the fully opened position (stop position).
On the other hand, a braking effort (braking force) is electrically or magnetically applied onto the electrically controlled stepping motor so that the rotor may stop rotating at a given position. Therefore, at the fully closed position, the above-described inertial force and the braking force collide with each other to induce a vibrating state (the hunting) in moving directions of the sectors 101 and 107. If the sectors 101 and 107 vibrate in this manner, the sectors are misaligned from a predetermined fully closed position and let the light come in the opening 100 (hereinafter, referred to as reexposure state). It is impossible to capture an image appropriately by use of the optical apparatus, such as a camera, having the shutter apparatus that cannot shield the light completely on an originally configured fully closed position.